The present invention relates to a photovoltaic device, and more particularly relates to a photovoltaic device including a laminated product (pin junction) of a p-type amorphous layer, an i-type amorphous layer and an n-type microcrystalline layer.
FIG. 1 is a structural view of a conventional photovoltaic device having a laminated product of a p-type amorphous layer, an i-type amorphous layer and an n-type microcrystalline layer. In FIG. 1, numeral 31 is a transparent substrate. A transparent conductive film 32, a p-type amorphous silicon layer 33, an i-type amorphous silicon-layer 34, an n-type microcrystalline silicon layer 35 and a back electrode film 36 are laminated in this order on the transparent substrate 31.
In a photovoltaic device having such a structure, each of the silicon layers 33, 34 and 35 is usually deposited by a plasma CVD process. In this case, there is a possibility that peeling occurs between the amorphous layer and the microcrystalline layer due to stress generated at the time when the layers are cooled to room temperature from the deposition temperature. The cause of peeling will be described below.
FIG. 2 is a conceptual view of stress generated in this silicon laminated product. The stress includes internal stress which is caused by a structural change between the amorphous layer and the microcrystalline layer, and thermal stress which is generated when cooling the layers deposited in a high temperature condition to room temperature. In the case of hydrogenated amorphous silicon (a-Si:H) deposited by the plasma CVD process, it has been known that the internal stress refers to compressive stress for the amorphous layer in which the SiH2 bond content is smaller than the SiH bond content, while the internal stress refers to tensile stress for the microcrystalline layer in which the SiH2 bond content is greater than the SiH bond content. In contrast, since the thermal stress is proportional to the difference in the thermal expansion coefficient between the respective layers, tensile stress proportional to the deposition temperature is generated in a thin film that was cooled to room temperature after being deposited in a high temperature condition of not lower than 100xc2x0 C.
Peeling of the silicon layers does not occur immediately after the deposition thereof at high temperatures, but occurs just after they have been cooled to room temperature. It would therefore be supposed that peeling occurs when the amorphous layer as an under layer is creased by thermal stress (tensile stress) generated in the microcrystalline layer.
Thus, the conventional photovoltaic device including the laminated product of the amorphous layers and microcrystalline layer suffers from a problem that film peeling occurs between the amorphous layer and the microcrystalline layer.
It is an object of the present invention to provide a photovoltaic device in which film peeling does not occur between an amorphous layer and a microcrystalline layer.
A photovoltaic device according to the first aspect includes at least one laminated product made by laminating a p-type amorphous layer, an i-type amorphous silicon layer, and an n-type microcrystalline layer in which the volume fraction of crystal phase is not less than 30% and the SiH2 bond content is greater than the SiH bond content, wherein the laminated product satisfies the conditions of
50 xc3x85 less than dc1 less than da1xc3x97xcex11xe2x80x83xe2x80x83(1)
and
0.124  less than xcex11 less than 0.130xe2x80x83xe2x80x83(2),
where
da1 is the total thickness (xc3x85) of the p-type amorphous layer and i-type amorphous silicon layer, and
dc1 is the thickness (xc3x85) of the n-type microcrystalline layer.
A photovoltaic device according to the second aspect includes at least one laminated product made by laminating a p-type amorphous layer, an i-type amorphous silicon germanium layer, and an n-type microcrystalline layer in which the volume fraction of crystal phase is not less than 30% and the SiH2 bond content is greater than the SiH bond content, wherein the laminated product satisfies the conditions of
30 xc3x85 less than dc2 less than da2xc3x97xcex12xe2x80x83xe2x80x83(3)
and
0.079  less than xcex12 less than 0.083xe2x80x83xe2x80x83(4),
where
da2 is the total thickness (xc3x85) of the p-type amorphous layer and i-type amorphous silicon germanium layer, and
dc2 is the thickness (xc3x85) of the n-type microcrystalline layer.
A photovoltaic device according to the third aspect includes: at least one first laminated product made by laminating a p-type amorphous layer, an i-type amorphous silicon layer, and an n-type microcrystalline layer in which the volume fraction of crystal phase is not less than 30% and the SiH2 bond content is greater than the SiH bond content; and at least one second laminated product made by laminating a p-type amorphous layer, an i-type amorphous silicon germanium layer, and an n-type microcrystalline layer in which the volume fraction of crystal phase is not less than 30% and the SiH2 bond content is greater than the SiH bond content, wherein the laminated products satisfy the conditions of the above expressions (1) to (4).
According to the photovoltaic device of the present invention, in the laminated product made by laminating a p-type amorphous layer, an i-type amorphous silicon layer and an n-type microcrystalline layer and/or the laminated product made by laminating a p-type amorphous layer, an i-type amorphous silicon germanium layer and an n-type microcrystalline layer, the thickness of each of the layers is set as described above. With this settings, it is possible to reduce the effect of thermal stress (tensile stress) generated in the n-type microcrystalline layer and prevent film peeling.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.